High speed data service has become a ubiquitous part of modern life, and the availability of such service is of ever-increasing importance. Typically, numerous data service subscribers send and receive data through a service provider. The subscribers may be individual homes or businesses and the service provider may be a separate entity, though this need not be the case. Subscriber data service is often provided over a physical medium that is also used to provide other types of service. One well-known example is the provision of data service over a coaxial cable that is also used to provide cable television (CATV) service. In many CATV systems, a first portion of the radio frequency spectrum is used for CATV service, a second portion used for upstream data transmissions from subscribers to a head end, and a third portion used for downstream data communications from the head end to the subscribers. The communicated data may include emails, communications to and from the Internet, voice over IP (VoIP) telephone service, video on demand (VOD), etc.
Existing subscriber network architectures pose ongoing challenges. For example, combined CATV and subscriber data systems are often designed to comply with the Data over Cable Service Interface Specifications (DOCSIS) group of standards promulgated by Cable Television Laboratories, Inc. A DOCSIS head end includes a cable modem termination system (CMTS) that sends and receives communications to individual subscribers. Under later versions of the DOCSIS standards, the CMTS functions may be divided between a modular CMTS (M-CMTS) core and one or more Edge Quadrature Amplitude Modulation (EQAM) devices. Because of the manner in which functions are divided between an M-CMTS core and EQAMs, the separation between these devices is usually limited to several hundred feet. This can significantly constrain design of cable systems.
The relative expense of an M-CMTS core relative to an EQAM and the distribution of functions between an M-CMTS core and EQAM can inhibit system scalability. In particular, adding additional system capacity requires adding additional M-CMTS cores and additional EQAMs. The additional M-CMTS cores are needed so as to accommodate increased demand for certain functionality, but other functionality of the additional M-CMTS core(s) may not be needed. Other scalability, operational and environment issues can also arise. Using known architectures, additional equipment for increasing QAM channels could result in large space requirements, considerable increases in heating and cooling requirements, and a significant increase monitoring, management and support requirements.
FIG. 1 is a block diagram generally showing a network architecture currently employed by cable system operators. The various blocks in FIG. 1 correspond to categories of network elements, and the arrows connecting those blocks indicate flows of data between those network element categories. For example, data corresponding to services is received from and sent to one or more backbone IP networks 1001 by routers represented by block 1002. Service data includes both broadcast data (e.g., television and cable network programming), narrowcast data (e.g., VOD and switched digital video (SDV) programming) and unicast data (e.g., high speed data (HSD) service providing Internet connectivity to individual subscribers and VoIP or other type of telephone service). The backbone network may be, e.g., a system operator's national IP network, the Internet, some combination of the Internet and a system operator's network etc. Typically, several layers of routers (e.g., at the national, regional and local levels) are part of block 1002. Broadcast and narrowcast data is routed to universal edge QAM (quadrature amplitude modulation) devices (UEQAMs) that are typically located in distribution hubs, which devices are represented in FIG. 1 by block 1003. Unicast data is routed to and from cable modem termination system (CMTS) cores 1004, with those CMTS cores also typically located in distribution hubs. Downstream unicast data is sent from CMTS cores to UEQAMs. The UEQAMs then modulate the broadcast, narrowcast and unicast downstream data into RF frequency channels that are combined (block 1005) and communicated to lasers 1006 for fiber optic transmission to individual service group nodes (block 1007). Those nodes convert the downstream optically-transmitted signals to electrical signals for distribution over coaxial cables to subscriber devices such as cable modems (CMs), set top boxes (STBs), media terminal adapters (MTAs), etc. Upstream transmissions from subscribers are received at nodes 1007, converted to optical signals and forwarded to CMTS cores, where those optical signals are converted to electrical signals and further processed.
The architecture of FIG. 1 was designed to support a few narrowcast and/or unicast channels in the presence of a large proportion of broadcast channels, both analog and digital. Such an architecture is optimized for combining at the RF layer, i.e., combining signals from (or to) many RF Ports. Each signal may contain an analog channel, a digital broadcast video multiplex QAM, or a small number of High Speed Data (HSD) channels. Architectures such as are shown in FIG. 1 can be unduly restrictive and/or pose problems if a cable system operator wishes to change the mix of available services.